A scientist has 20 grams of the radioactive isotope sodium-24. The isotope decays exponentially as shown in the table.
Time (hours)
Mass (grams)
5
15.9
10
12.6
15
10
20
7.9
25
6.3
30
5
Approximately what will the mass of the isotope be after 45 hours?
A 1.5 grams
B. 2.5 grams
C. 3.5 grams
D. 4.5 grams